The proposed research continues investigation of the characteristics and causes of sensorineural hearing loss. One group of experiments will concentrate on auditory misperception associated with both cochlear and retrocochlear malfunction in persons whose hearing problems have etiologies that are reasonably certain. Misperceptions to be studied include not only loss of sensitivity, as manifested by deterioration in the ability to detect simple tones or complex acoustic signals such as speech in quiet and in the presence of competing sounds, but also a decreased ability to make discriminations among signals differing in intensity, frequency, spectral complexity, or temporal pattern. Where possible, these characteristics will be related to histopathological analyses of temporal bones from patients with similar etiologies. To confirm and supplement these results, experimental animals, chiefly chinchillas, will be used to study the relations between (A) exposures to steady or intermittent noise, administration of chemical toxins (injected or applied topically in the middle ear), and/or mechanical cochlear trauma, and (B) the resulting changes in behavioral auditory capabilities and in the electrophysiological, neurophysiological, structural, and ultrastructural characteristics of the cochlea. Changes in vestibular function associated with certain types of hearing loss and with drugs that are not only ototoxic but also vestibulotoxic will also be determined. The results of these series of experiments will advance our understanding of the mechanisms of hearing loss, thereby improving the accuracy of differential diagnosis of auditory disorders and leading ultimately to better methods for their management.